Fix DownloadDirectoryAdapter ImageView ID

The ImageView id in modern_list_item_view was changed from "icon_view"
to "start_icon" (https://crrev.com/c/2024495) causing an NPE when the
"Download file" dialog's dropdown is clicked.

Bug: 1047883
Change-Id: I656562af3af4ada9e602c176c5d10abc035c9b4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2033929
Commit-Queue: Natalie Chouinard <chouinard@chromium.org>
Reviewed-by: Brandon Wylie <wylieb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737541}

chrome/android/java/src/org/chromium/chrome/browser/settings/download/DownloadDirectoryAdapter.java

@@ -145,7 +145,7 @@ public class DownloadDirectoryAdapter extends ArrayAdapter<Object> {
             }
         }
 
-        ImageView imageView = view.findViewById(R.id.icon_view);
+        ImageView imageView = view.findViewById(R.id.start_icon);
         imageView.setVisibility(View.GONE);
 
         return view;